Re: [PATCH 1/2] iomap: add a swapfile activation function

[Jan Kara <jack@suse.cz>]

On Wed 02-05-18 13:32:28, Darrick J. Wong wrote:
> +/*
> + * Collect physical extents for this swap file.  Physical extents reported to
> + * the swap code must be trimmed to align to a page boundary.  The logical
> + * offset within the file is irrelevant since the swapfile code maps logical
> + * page numbers of the swap device to the physical page-aligned extents.
> + */
> +static int iomap_swapfile_add_extent(struct iomap_swapfile_info *isi)
> +{
> +	struct iomap *iomap = &isi->iomap;
> +	unsigned long nr_pages;
> +	uint64_t first_ppage;
> +	uint64_t first_ppage_reported;
> +	uint64_t last_ppage;
> +	int error;
> +
> +	/*
> +	 * Round the start up and the length down so that the physical
> +	 * extent aligns to a page boundary.
> +	 */
> +	first_ppage = ALIGN(iomap->addr, PAGE_SIZE) >> PAGE_SHIFT;
> +	last_ppage = (ALIGN_DOWN(iomap->addr + iomap->length, PAGE_SIZE) >>
> +			PAGE_SHIFT) - 1;
> +	nr_pages = last_ppage - first_ppage + 1;

So if I pass in iomap->addr = 1k, iomap->length = 1k, I get first_ppage =
1, last_ppage = -1, and thus nr_pages = (unsigned long)-1 and the test
below does not hit although it should. I think you need there

	if (first_ppage > last_ppage)

Otherwise the patch looks good to me.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR